Method and device for etching a thin conductive layer which is disposed on an insulating plate such as to form an electrode network thereon

ABSTRACT

The invention relates to a method and device for etching a thin conductive layer which is disposed on an insulating plate such as to form an electrode network thereon. Before the etching takes place, a protective film, comprising patterns corresponding to the electrodes in the network, is applied, said film being removed after etching. The inventive etching method consists in: moving the plate in the general direction of the electrodes to be formed; circulating an electrochemical bath in a shear zone which is defined by the surface of the layer to be etched and by the surface of a counter electrode; and passing an electric current between the counter electrode and the zones which are not protected by the protective film, said current being conveyed over a line of contacts which is disposed on the surface of the conductive layer perpendicularly to the direction of passage D. In this way, etching homogeneity and network formation precision are improved.

The invention relates to a method and to a device for etching a thinconductive layer based on tin oxide, chromium oxide, indium oxide or amixture of at least two of these oxides, this being deposited on aninsulating plate so as to form an array of conductive electrodes on thissubstrate.

To produce an array of electrodes on an insulating plate, for example aglass plate, it is sometimes more advantageous and/or more economical toapply the uniform conductive layer to this plate and then etchelectrodes in this layer than to apply electrodes directly to the plate.

This is the case, for example, in the production of transparentconductive electrodes on a glass plate or panel intended to form thefaceplate of a plasma display: the starting point is then a glass platecovered with a transparent conductive layer based on tin oxide obtainedby pyrolytic means; tin oxide layers may thus be produced directly, inline, on glass as it leaves a glass plate manufacturing plant; tinoxide, generally doped with fluorine, is deposited when the glass isstill at a temperature of around 600° C., by pyrolytic decomposition ofa tin compound; the tin oxide layer obtained has at least three majoradvantages:

-   -   the resistivity of the conductive layer is low enough to be able        to form an array of electrodes on the faceplate of a plasma        panel; it is generally between 10 and 25 ΩQ/ ;    -   the conductive layer obtained is chemically extremely stable;        thus, this layer suffers no deterioration when a dielectric        enamel layer, needed for the operation of the plasma panel, is        deposited on this layer and baked; and    -   compared to vacuum sputtering deposition used elsewhere for        forming arrays of transparent electrodes, this deposition method        is very inexpensive.

However, this method of producing transparent electrodes has a majordrawback because the electro-chemical etching of this layer isparticularly difficult to control in an industrial line when veryprecise geometries are to be obtained.

More specifically, the above method, which is used to etch electrodes,conventionally comprises the following steps:

-   -   a protective film having the same patterns as that of said array        of electrodes is applied to the conductive layer;    -   the plate provided with the protective film is run through an        electrochemical etching bath;    -   during the run through, with a counterelectrode immersed in the        etching bath, an electric current is made to flow through said        bath between said counterelectrode and the immersed areas of the        conductive layer of said plate that are unprotected by the film;        and    -   the protective film is removed.

Such a method and a device for implementing it are, for example,described in the following documents:

-   -   the article entitled “Electrochemical patterning of tin oxide        films” by B. J. Baliga in Journal of the Electrochemical Society        1977, Vol. 124, No. 7, pp. 1059-1060;    -   the article entitled “Micromachining of tin oxide by        electrochemical reduction process” by Y. Matsuo et al., in        Journal of the Electrochemical Society, 1998, Vol. 145, No. 9,        pp. 3067-3069; and    -   the following patent applications: U.S. Pat. No. 3,205,155, U.S.        Pat. No. 3,507,759, U.S. Pat. No. 3,668,089, U.S. Pat. No.        4,165,989, U.S. Pat. No. 5,227,036 and JP 06-293278.

The nature and the temperature of the bath, the run speed and thecurrent flow conditions are described in these documents.

The drawback of the devices for carrying out the electrochemical etchingprocess, such as those described in the abovementioned documents, isthat they do not allow sufficiently uniform etching of the areas of theconductive layer to be etched and do not allow narrow electrodes with asufficiently precise outline to be formed; the problem is particularlycrucial in the case of conductive layers based on tin oxide that areobtained by pyrolysis.

This is because the electrochemical electro-erosion current must be fedinto the immersed areas with the thin conductive layer via a currentfeed electrode in contact with this layer; between the various areas ofelectrical contact of the thin layer with this electrode and the variousareas of this layer being etched in the bath, the current paths havedifferent lengths; since the resistivity of this layer is notinsignificant, the shortest current paths become preferential paths,thereby resulting in preferential etching areas; this effect isexacerbated by the thinning of the areas in this layer over the courseof etching.

The object of the invention is to avoid the aforementioned drawbacks.

For this purpose, the subject of the invention is a method for etching athin conductive layer deposited on an insulating plate, so as to form onthis plate an array of conductive electrodes in this layer, comprisingthe steps in which:

-   -   before etching, a protective film, having patterns corresponding        to the electrodes of said array of electrodes, is applied to        said conductive layer;    -   for the etching, the unprotected areas of the surface of said        conductive layer are brought into contact with an        electrochemical etching bath and, with a counterelectrode        immersed in this bath, an electric current is made to flow        through said bath between said counterelectrode and said        unprotected areas so as to etch these areas over the entire        thickness of said layer;        characterized in that, during the etching:    -   said plate is made to run in a direction corresponding to the        general direction of the electrodes to be formed;    -   to make the electric current flow through the bath, the electric        current is fed into said unprotected areas along a contact line        that are located on the surface of the conductive layer and        cutting the run direction; and    -   said bath is made to circulate through a bath shear zone bounded        by the surface of the layer to be etched and by the active        surface of said counterelectrode.

In general, after etching, said protective film is removed.

Most of the electrodes of the array, whether they are in the form ofstraight lines or form circuitous paths, and whether or not they areprovided with branches, have a common general direction; according tothe invention, it is approximately along this direction that the plateis made to run; thanks to this arrangement, the electric current may befed from the contact line right into the unprotected areas immersed inthe bath without any electrical discontinuity, especially across theelectrodes being formed.

The term “active surface of the counterelectrode” is understood to meanthe main surface of this counterelectrode which is immersed in the bath,through which main surface most of the electric current passes.

By circulating the bath through the areas of high current density, thatis to say in the shear zone, the efficiency and uniformity of theetching are substantially improved.

This way in which the plate runs, this way in which the current is fedand in which the bath is circulated therefore contribute to theuniformity and to the precision of the etching; it is thus easy toobtain an array of electrodes having outlines that are very accuratelydefined and it is easily possible to produce electrodes of narrow widthand/or of complex shapes.

Preferably, the distance between the contact line and that section ofthe bath shear zone closest to this line is constant over the entirewidth of the area to be etched.

Thus, the electric current is uniformly distributed over eachunprotected area (4) in contact with the bath and during etching; theuniformity of the etching and the precision in the outline of theelectrodes of the array are also improved.

According to the most common and simplest arrangement for implementingthe method according to the invention:

-   -   said contact line is straight and perpendicular to the run        direction;    -   the direction of circulation of the bath through the shear zone        coincides with said run direction, in the same sense or in the        opposite sense; and    -   the shear zone has an approximately constant thickness over the        entire width of the area to be etched.

The expression “thickness of the shear zone” is understood to mean thedistance between the surface of the layer to be etched and the activesurface of the counterelectrode.

Preferably, the distance between said contact line and that section ofthe bath shear zone closest to this line is less than 5 cm.

The lines of current flowing through the conductive layer toward thebath are then considerably shortened, thereby reducing ohmic losses inthe conductive layer.

Preferably, the bath shear zone also has an approximately constantthickness along the run direction, over a distance correspondingapproximately to the width of the active surface of saidcounterelectrode.

The width of the shear zone therefore corresponds to that of thecounterelectrode; together with the run speed, it determines the maximumtime required to etch each surface element to be etched; the width ofthe counterelectrodes may therefore advantageously be adapted to thedesired run speed and to the desired etching time.

Preferably, the thickness of said shear zone is between 0.1 mm and 5 mm.

There is a better compromise between a high shear rate of the bath,favorable to etchping efficiency, and the risks of a short circuit as itruns between the surface to be etched and the counterelectrode.

Preferably, the flow of the bath circulating through said shear zone isdistributed approximately uniformly over the entire width of the area tobe etched.

The uniformity of the etching is thus improved.

The invention may also have one or more of the following features:

-   -   the thin conductive layer is based on tin oxide, chromium oxide,        indium oxide or a mixture of at least two of these oxides;    -   the thin conductive layer is deposited on the insulating plate        by pyrolytic means;    -   the electrochemical etching bath comprises at least one acid        chosen from the group consisting of hydrochloric acid, sulfuric        acid, nitric acid, chromic acid, acetic acid and formic acid;    -   the counterelectrode serves as anode;    -   the mean electric current density in the conductive layer in        contact with the bath is greater than 1 A/dm², preferably        greater than 10 A/dm²;    -   the temperature of said bath is greater than or equal to 30° C.;        and    -   the insulating plate is made of glass.

The subject of the invention is also a device for etching areas of athin conductive layer placed on an insulating plate, which can be usedfor implementing the etching step of the method as claimed in any one ofthe preceding claims, comprising:

-   -   means for making this plate run along a plane run path so that        the surface to be etched is brought into contact with the        etching bath;    -   means for feeding an electric current into said conductive layer        before contact with the bath;    -   a counterelectrode, immersed in said bath, for return of the        electric current;    -   means for making an electric current flow through said bath        between said current feed means and the current return        counterelectrode;        characterized    -   in that the electric current feed means comprise a rail suitable        for coming into contact with the surface of said conductive        layer of the plate along the run path, this rail being placed in        such a way that the contact line of this rail on this layer cuts        this run path; and    -   in that it furthermore includes means for making the bath        circulate between the active surface of the counterelectrode and        the run path, this bath circulation zone forming a shear zone        having an upstream opening and a downstream opening of the run        path.

Preferably, the rail is adapted so that the distance between saidcontact line and that section of the shear zone closest to this line isconstant over the entire width of the area to be etched; depending onthe sense of the bath circulation, this closest zone corresponds eitherto the upstream opening or to the downstream opening of the run path.

According to the most common and simplest arrangement, in the deviceaccording to the invention:

-   -   said rail is straight and perpendicular to the run direction;    -   the distance between the active surface of the counterelectrode        and the run path is approximately constant over the entire width        of the area to be etched; and    -   the means for making the bath circulate are designed to make the        bath circulate through the shear zone along the same direction        as that in which the plate runs, in the same sense or the        opposite sense.

Preferably, the distance between said contact line and that section ofthe shear zone closest to this line is less than 5 cm.

Preferably, the active surface of the counterelectrode has a plane mainpart lying parallel to the run path.

Preferably, the distance between the active surface of thecounterelectrode and the run path is between 0.1 mm and 5 mm.

Preferably, the means for making the bath circulate includebath-stream-distributing means suitable for obtaining a constant bathflow rate over the entire width of the openings of the shear zone.

Preferably, the bath circulation means comprise an ejection nozzle thatextends at least over the entire width of the layer to be etched and itsopening is directed toward one of the openings of the shear zone.

Preferably, the circulation means are suitable for forcing the bathejected by the nozzle to circulate through said shear zone.

Preferably, the device according to the invention comprises means forrecovering the bath exiting one of the openings of the shear zone andmeans for recirculating the recovered bath.

Preferably, the device according to the invention comprises means forwiping the etched surface on exiting the bath.

The object of the invention is also the use of the method and/or of thedevice according to the invention for manufacturing the front panel orfaceplate of a display, which panel is provided with at least one arrayof electrodes; preferably, the manufacture of said panel then comprisesthe application of a dielectric enamel layer to said array and thebaking of this enamel layer.

The invention will be more clearly understood from reading thedescription that follows, given by way of non-limiting example and withreference to the appended figures in which:

FIG. 1 shows a cross-sectional view of a preferred embodiment of thedevice according to the invention; and

FIG. 2 shows a perspective view of a running plate and of a circulatingbath in the device according to FIG. 1.

Referring to FIG. 2, an insulating glass plate 1 comprises, on its lowerface, a conductive layer 2 based on tin oxide, deposited in this case bypyrolytic means, in which layer it is desired to etch an array ofelectrodes; the thickness of this layer is around 400 nm and itsresistivity is around 15 Ω/(ohms/square).

The conductive layer 2 is coated in a manner known per se with aprotective film 3 having patterns that correspond to the electrodes ofthe array to be etched; between the patterns in this film 3, thesurfaces unprotected by the film form areas 4 of the conductive layer tobe etched; the areas to be etched are distributed over the entire widthof the plate, which thus forms the overall width of the area to beetched.

The protective film (with its patterns) is applied in a manner known perse. In particular, it may be applied by photolithography or by screenprinting; its thickness is generally between 5 and 30 μm; thecomposition and the adhesion of this film are adapted so as to withstandthe electrochemical etching operations that will be described below.

As shown in FIG. 1, and also in FIG. 2, the etching device according tothe invention has, according to a preferred embodiment, the followingcomponents:

-   -   means for making the plate 1 run in the direction and the sense        that are indicated by the arrow D, along a plane run path; these        means comprise here running rolls 5 a, 5 b, 5 b′, 5 c that are        actuated in a manner known per se in the direction of rotation        indicated by the arrows and define the run path of the plate;        hereafter, the plane of the run path corresponds more precisely        to that of the conductive layer, that is to say to the lower        surface of the plate;    -   a fixed transverse member 6 extending at least over the entire        width of the layer to be etched, that surface 61 of the        transverse member that is closest to the run path defines, with        this path, a shear zone 7 having an approximately constant        thickness Ec; here, the transverse member 6 is straight and lies        perpendicular to the run direction; here, the surface 61 is        plane and parallel to the run path in such a way that the shear        zone 7 also has a constant thickness Ec along the run path; the        shear zone 7 therefore forms a rectangular parallelepiped        forming a duct for circulation of the etching bath, said duct        having an upstream opening 8 and the downstream opening 9;    -   means for making an etching bath circulate through this shear        zone 7 in the run direction, here in the same sense as the run        direction, in such a way that the etching bath penetrates this        zone via the upstream opening 8 that serves as inlet and exits        said zone via the downstream opening 9 that serves as outlet;        these means comprise an ejection nozzle that extends over at        least the entire width of the layer to be etched and the opening        of which is directed toward one of the openings of the shear        zone, in this case the upstream opening 8; preferably, as shown        in FIGS. 1 and 2, the opening of the ejection nozzle coincides        with the opening 8 of the shear zone 7, so as to force the bath        ejected by this nozzle to circulate through the shear zone 7;        other embodiments, without forced circulation, are conceivable        without departing from the invention;    -   means for feeding an electric current into the conductive layer        4 before it comes into contact with the bath in the shear zone        7, these means consequently being positioned on the run path        upstream of this shear zone 7; these means comprise a fixed rail        11 comprising contactors 12 that are intended to come into        direct contact with the unprotected areas 4 of the conductive        layer 2 of the plate 1 on the run path, said rail being placed        in such a way that the contact line 13 of these contactors cuts        this run path and lies over the entire width of the layer to be        etched; these contactors 12 here are also in contact with the        protective film 3, in the covered areas and the protected areas        of the conductive layer 2; since the rail 11 here is straight        and lies perpendicular to the run direction, the contact line 13        is also straight and perpendicular to the run direction; here,        the rail 11 is fastened to the transverse member 6 by fastening        means 14;    -   a counterelectrode 10 for return of the electric current,        fastened to the transverse member 6, the active surface of which        counterelectrode forms at least one part of the surface 61        closest to the run path of the transverse member 6; this        counterelectrode 10 being made of conductive material;    -   means (not shown) for making an electric current flow through        the bath that circulates through the shear zone 7 between the        current feed rail 11 and the counterelectrode 10.

In this stripping device, the section of the bath shear zone nearest tothe contact line 13 corresponds, in this case, to the upstream opening 8of the shear zone 7.

Since the transverse member 6 here supports both the current feedcontact rail 11 and the current return counterelectrode 10, thistransverse member 6 here is made of insulating material.

According to the embodiment in FIG. 1, the transverse member 6 alsoserves as nozzle for ejecting the bath into the shear zone 7; for thispurpose, it includes an internal cavity 18 for distributing the streamemerging in at least one duct bounded by a plate 15 secured to thetransverse member 6, which duct in turn emerges via the ejection nozzlein the upstream opening 8 of the shear zone 7; this cavity 18 issupplied by a bath feed pipe 16 in turn connected to bath recirculationmeans (not shown); the cavity 18 makes it possible to obtain a constantbath flow rate over the entire width of the opening 8; a mesh 17 (orseveral such meshes) is placed across this cavity 18 in order to furtherimprove the uniform distribution of the flow over the entire length ofthe bath ejection nozzle; in the entire section of the shear zone of thebath perpendicular to the run direction, the bath flow rate per unitlength of this section is thus approximately constant over the entirewidth of the area to be etched; other bath-distributing means may beused without departing from the invention.

The counterelectrode 10 extends over the entire width of the device and,in the run direction, over an active width that may be adjustable; inorder to adjust it, various sets of counterelectrodes having differentwidths may be used; the counterelectrode 10 is made of titanium forexample; the active surface 61 may be formed from a thin layer ofplatinum, for example with a thickness of around 5 μm; the use ofplatinum prevents passivation.

Preferably, the thickness Ec of the shear zone 7 is between 0.1 and 5mm, for example equal to 3 or 4 mm.

Advantageously as shown in FIG. 1, the distance that separates thecontact line 13 of the upstream opening 8 from the bath shear zone 7(see FIG. 2) is between 1 and 5 mm; referring to FIG. 1, this distancehere depends on the thickness of the plate 15 that defines the bathejection nozzle duct; this plate 15 is made of insulating material inorder to prevent the current from passing directly between thecontactors 12 and the bath.

Without departing from the invention, the contactors 12 may bepositioned a certain distance from the plate 15; the plate 15 thenserves as a “nonreturn blade”.

The contactors 12 supported by the rail 11 may, for example, be formedfrom graphite fibers or carbon fibers; the diameter of these fibers ispreferably substantially smaller than the width of the areas to beetched.

The etching device also includes means (not shown) for recovering thebath exiting the shear zone via the downstream opening 9, hence enablingthe bath to be reinjected into the recirculation means.

Finally, at the exit of the shear zone 7, the etching device includeswiping means 19 that are suitable for removing the bath entrained by therunning plate, or indeed also to remove any solid residue from theconductive layer to be etched; these means comprise here a brush roll 20and a backing roll 21.

According to a variant of the invention, the device includes, also atthe exit of the shear zone 7, means for removing the protective film 3from the surface of the running plate, for example by spraying analkaline bath onto this film.

The etching or etching step of the method according to the inventionwill now be described.

An etching bath is prepared by adapting its composition to the nature ofthe conductive layer to be etched, in accordance with the teachings ofthe documents mentioned above in the introduction; in the case of alayer based on pyrolytic tin oxide with a thickness of 0.4 μm, a 5 wt %hydrochloric acid bath at room temperature is used for example.

The run speed of the plate 1 is defined in such a way that the residenttime of this plate in the shear zone 7 is long enough to etch theunprotected areas of the conductive layer over its entire thickness; itmay therefore be seen that the maximum run speed permitted depends onthe etching conditions and the nature and thickness of the conductivelayer to be etched; in practice, the run speed may be between 0.1 and 2m/min, for example around 0.2 to 0.3 m/min.

While the plate 1 with its downwardly directed conductive layer 2 isrunning, the etching bath is injected using bath recirculation meansinto the shear zone 7 across the transverse member 6 and the ejectionnozzle; the arrows Be and Bs in FIG. 2 indicate the circulation of thebath through the shear zone 7.

While the plate 1 is running and the etching bath is circulating throughthe shear zone 7, an electric current is made to flow between the rail11 and the counterelectrode 10; the succession of electric contactsbetween the contactors 12 carried by the rail and the unprotected areas4 to be etched, which are arranged between the patterns of theinsulating film 3 and distributed along the rail, forms the contact line13 which cuts the run path of the plate 1; starting from these contacts,the electric current is conducted into the thickness of the conductivelayer as far as portions of areas 4 to be etched that are in contactwith the bath; the electric current then passes through the bath overthe thickness Ec of the shear zone, between the surface of the areas 4to be etched that are in contact with the bath and the active surface 61of the counterelectrode; the current lines are therefore particularlyshort, this having the advantage of limiting ohmic losses; the electriccurrent fed to the rail 11 may exceed 5 A/dm, generally at a maximumvoltage of 20 V between the rail 11 and the counterelectrode 10; thus,for a counterelectrode width of 2 cm, the current density may exceed 25A/dm²; to achieve effective etching, the current density is preferablygreater than 1 A/dm², or even greater than 10 A/dm².

Preferably, the rail 11 serves as cathode and the counterelectrode 10serves as anode, as shown in FIG. 1.

Good etching results have been obtained on a layer of pyrolytic tinoxide 0.4 μm in thickness using a 5 wt % HCl solution at roomtemperature under the following conditions: shear zone thickness Ec=3mm; width of the plate to be etched=600 mm; bath flow rate around 10l/min in this zone; counterelectrode width=2 cm, the counterelectrodeserving as anode; run speed=0.3 m/min; the electric current=35 A;distance between the contact line 13 and the upstream opening 8 of theshear zone=5 mm.

It should be noted that the reduced distance between the contact line 13and the upstream opening 8 of the shear zone is an important factor inlimiting ohmic losses; this distance is preferably less than 5 cm, oreven, if possible, as in this case, less than 1 cm.

At the run exit, the wiping means remove the bath entrained on the lowersurface of the plate.

What is then obtained is a plate provided with an array of conductiveelectrodes covered with a protective film; this protective film is thenremoved from the etched plate in a manner known per se.

According to a variant of the invention, when the electrodes to beetched are intended to be coated with an insulating layer, especially inthe case of plasma panels, the protective film may, on the contrary stayin place; the protective film used is then matched to the insulatinglayer that it is desired to form on the electrodes; in the case ofplasma displays, this film then generally comprises a dielectric mineralcomposition; after the panel provided with its array of electrodes hasbeen baked, the electrodes are then coated with a dielectric layer.

The method that has just been described makes it possible to achieveuniform etching of the conductive layer over the entire width of theplate and thus obtain electrodes that are narrow and/or of complex shapewith a high etch rate; it has thus been possible to etch arrays ofelectrodes at rates of more than 50 cm/min; this method is particularlybeneficial when the conductive layer to be etched is based on pyrolytictin oxide; thanks to the invention, an array of electrodes can be etchedreally easily and precisely in this type of layer.

Without departing from the invention, it is possible to use a device inwhich, unlike that described above, the plate 1 to be etched is fixedand it is the transverse member 6 that moves.

The method according to the invention is also applicable to otherinsulating plates provided with a conductive layer, provided that theconductive layer can be etched and etched by an electrochemical method;instead of being made of glass, the plate may, for example, be made ofceramic or glass-ceramic; this plate may be provided with anotherconductive layer on the other face; instead of being made of pyrolytictin oxide, the conductive layer to be etched may in particular be basedon nonpyrolytic tin oxide, on indium oxide or on a mixture of these twooxides (ITO).

The plate provided with its array of electrodes obtained by the methodaccording to the invention can advantageously be used in any type ofdisplay panel having a panel provided with at least one array ofelectrodes, especially plasma displays, liquid-crystal displays andlight-emitting diode displays, such as OLED displays; when theelectrodes thus etched are transparent, this plate then advantageouslyserves for the manufacture of the front panel of the display.

To manufacture the front panel of a plasma display, a layer ofdielectric enamel is applied to the array of electrodes on this plateand is then baked; when the initial conductive layer is based onpyrolytic tin oxide, no impairment of the array of electrodes uponbaking the dielectric enamel is observed.

1. A method for etching a thin conductive layer deposited on aninsulating plate, so as to form on this plate an array of conductiveelectrodes in this layer, comprising the steps in which: before etching,a protective film, having patterns corresponding to the electrodes ofsaid array of electrodes, is applied to said conductive layer; for theetching, the unprotected areas of the surface of said conductive layerare brought into contact with an electrochemical etching bath and, witha counterelectrode immersed in this bath, an electric current is made toflow through said bath between said counterelectrode and saidunprotected areas so as to etch these areas over the entire thickness ofsaid layer; wherein, during the etching: said plate is made to run in adirection corresponding to the general direction of the electrodes to beformed; to make the electric current flow through the bath, the electriccurrent is fed into said unprotected areas along a contact line that arelocated on the surface of the conductive layer and cutting the rundirection; and said bath is made to circulate through a bath shear zonebounded by the surface of the layer to be etched and by the activesurface of said counterelectrode.
 2. The method as claimed in claim 1,wherein the distance between said contact line and that section of thebath shear zone closest to this line is constant over the entire widthof the area to be etched.
 3. The method as claimed in claim 2, wherein:said contact line is straight and perpendicular to the run direction;the direction of circulation of the bath through the shear zonecoincides with said run direction, in the same sense or in the oppositesense; and the shear zone has an approximately constant thickness overthe entire width of the area to be etched.
 4. The method as claimed inclaim 3, wherein the distance between said contact line and that sectionof the bath shear zone closest to this line is less than 5 cm.
 5. Themethod as claimed in claim 3, wherein the bath shear zone also has anapproximately constant thickness along the run direction, over adistance corresponding approximately to the width of the active surfaceof said counterelectrode.
 6. The method as claimed in claim 5, whereinthe thickness of said shear zone is between 0.1 mm and 5 mm.
 7. Themethod as claimed in claim 3, wherein the flow of the bath circulatingthrough said shear zone is distributed approximately uniformly over theentire width of the area to be etched.
 8. The method as claimed in claim1, wherein said thin conductive layer is based on tin oxide, chromiumoxide, indium oxide or a mixture of at least two of these oxides.
 9. Themethod as claimed in claim 8, wherein said thin conductive layer isdeposited on the insulating plate by pyrolytic means.
 10. The method asclaimed in claim 8, wherein the electrochemical etching bath comprisesat least one acid chosen from the group consisting of hydrochloric acid,sulfuric acid, nitric acid, chromic acid, acetic acid and formic acid.11. The method as claimed in claim 8, wherein said counterelectrodeserves as anode.
 12. The method as claimed in claim 8, wherein the meanelectric current density in the conductive layer in contact with thebath is greater than 1 A/dm².
 13. The method as claimed in claim 1,wherein the temperature of said bath is greater than or equal to 30° C.14. The method as claimed in claim 1, wherein said insulating plate ismade of glass.
 15. A device for etching areas of a thin conductive layerplaced on an insulating plate, which can be used for implementing theetching step of the method as claimed in claim 1, comprising: means formaking this plate run along a plane run path so that the surface to beetched is brought into contact with the etching bath; means for feedingan electric current into said conductive layer before contact with thebath; a counterelectrode immersed in said bath, for return of theelectric current; means for making an electric current flow through saidbath between said current feed means and the current returncounterelectrode; wherein: in that the electric current feed meanscomprise a rail suitable for coming into contact with the surface ofsaid conductive layer of the plate along the run path, this rail beingplaced in such a way that the contact line of this rail on this layercuts this run path; and in that it furthermore includes means for makingthe bath circulate between the active surface of the counterelectrodeand the run path, this bath circulation zone forming a shear zoneShaving an upstream opening and a downstream opening of the run path.16. The device as claimed in claim 15, wherein said rail is adapted sothat the distance between said contact line and that section of theshear zone closest to this line is constant over the entire width of thearea to be etched.
 17. The device as claimed in claim 16, wherein: saidrail is straight and perpendicular to the run direction; the distancebetween the active surface of the counterelectrode and the run path isapproximately constant over the entire width of the area to be etched;and the means for making the bath circulate are designed to make thebath circulate through the shear zone along the same direction as thatin which the plate runs, in the same sense or the opposite sense. 18.The device as claimed in claim 17, wherein the distance between saidcontact line and that section of the shear zone closest to this line isless than 5 cm.
 19. The device as claimed in claim 17, wherein theactive surface of the counterelectrode has a plane main part lyingparallel to the run path.
 20. The device as claimed in claim 19, whereinthe distance between the active surface of the counterelectrode and therun path is between 0.1 mm and 5 mm.
 21. The device as claimed in claim17, wherein the means for making the bath circulate includebath-stream-distributing means suitable for obtaining a constant bathflow rate over the entire width of the openings of the shear zone. 22.The device as claimed in claim 21, characterized in that wherein thebath circulation means comprise an ejection nozzle that extends at leastover the entire width of the layer to be etched and its opening isdirected toward one of the openings of the shear zone.
 23. The device asclaimed in claim 22, characterized in that wherein the circulation meansare suitable for forcing the bath ejected by the nozzle to circulatethrough said shear zone.
 24. The device as claimed in claim 15, whereinit comprises means for recovering the bath exiting one of the openingsof the shear zone and means for recirculating the recovered bath. 25.The device as claimed in claim 15, wherein it comprises means for wipingthe etched surface on exiting the bath.
 26. The use of the method ordevice as claimed in any one of claim 1 in the manufacture of the frontpanel or faceplate of a display, which panel is provided with at leastone array of electrodes.
 27. The use as claimed in claim 26, wherein themanufacture of said panel includes the application of a dielectricenamel layer to said array and the baking of this enamel layer.